Battery fast-charging and cooling system and method of operating same

ABSTRACT

Provided is a battery charging system comprising (a) at least one charging circuit to charge at least one rechargeable battery cell; (b) a heat source to provide heat that is transported through a heat spreader element, implemented fully or partially inside said at least one battery cell, to heat up the battery cell to a desired temperature Tc before or during battery charging; and (c) cooling means in thermal contact with the heat spreader element configured to enable transporting internal heat of the battery cell through the heat spreader element to the cooling means when the battery cell is discharged. Charging the battery at Tc enables completion of the battery in less than 15 minutes, typically less than 10 minutes, and more typically less than 5 minutes without adversely impacting the battery structure and performance.

FIELD

The present disclosure relates generally to the field of batteries and,in particular, to batteries that are fast rechargeable and relatedbattery charging systems.

BACKGROUND

Electric vehicles (EVs) are viewed as a promising solution to CO₂emission and climate change issues. Batteries have been at the heart ofthe rapidly emerging EV industry. Despite the dramatic drop in cost oflithium-ion batteries (LiBs) over the past decade (from higher thanUS$1,000/kWh to less than US$200/kWh), the EV market still accounts foronly ˜1% of annual light-duty vehicle sales. Range anxiety, the fearthat an EV may run out of battery power during a trip, has long beenregarded as a key reason for consumers' reluctance to adopt EVs. Thisissue of range anxiety is exacerbated by the notion that rechargingbatteries in an EV usually take much longer time to recharge thanrefueling internal combustion engine vehicles (ICEVs).

To be competitive with ICEVs, fast charging of EVs should beweather-independent and should be comparable in the required length oftime as refueling a gasoline car. Variations in temperatures indifferent geographic regions and different seasons of a given regionhave posed a challenge to fulfill the need to have fast charging of EVbatteries since EV batteries (e.g. lithium-ion batteries) can behavevastly different at different charging temperatures. In winter, half ofthe United States and most of Northern Europe has an average temperaturebelow 0° C. None of today's EV batteries allow for fast charging at lowtemperatures. For instance, according to the owner's manual, Nissan Leafcan be charged to 80% full in 30 min (˜2C charge rate) at roomtemperature, but would take >90 min (<C/1.5 charge rate) to charge thesame amount of energy at low temperatures. Such a long recharge time isconsidered as necessary to avoid lithium plating on anode materialsurfaces. Currently, LiBs typically use graphite as anode material,which has a lithium intercalation potential within 100 mV vs. Li/Li+.Under some extreme conditions, the large anode polarization can bringgraphite potential below the threshold for lithium plating.

The deposited lithium on anode material surfaces reacts quickly with theelectrolyte, resulting in irreversible capacity loss. Additionally, themetallic lithium can grow into dendrites, which can penetrate throughthe separator, reaching the cathode to induce internal shorting. Toprevent lithium plating, lithium-ion batteries are charged at very lowrate (C/10 or less) at low temperatures, which require an excessivelylong period of time to be fully charged.

One approach to solving this issue entails introducing electricalcurrent into the battery cell for resistance heating of the batterycell. As one example, this can be accomplished by heating up the batterycell through controlled pulse charging and discharging of the battery.As another example, a sheet of metal foil is implemented inside abattery cell to generate joule heat that raises the battery temperatureto a desired temperature for battery charging, as disclosed by Chao Y.Wang, et al (e.g. US Publication No. 20140285135; 20140295222;20140342194; 20150104681; 20150303444; and 20160268646).

However, such an approach of internal joule heating or resistanceheating has several major drawbacks. One major problem is the danger ofoverheating when the electric current is switched on, allowing a largeamount of current to reach a location in an extremely short period oftime, creating local hot spots that can significantly degrade or damagethe various component materials (anode, cathode, separator, andelectrolyte, etc.) of a cell. Under extreme conditions, the local heatmay cause the liquid electrolyte to catch fire, leading to fire andexplosion hazards. Another major issue is the requirement ofimplementing a complex electric circuit that controls both heating andbattery charging; this battery management system must allow for constanttemperature sensing and frequent switching between resistance-heating(e.g. through a metal foil) and electric charging of a battery cell.

Accordingly, a continuing need exists to reduce the charging time of arechargeable battery without negatively impacting the battery. An urgentneed exists for a battery that can be fast charged at all climateconditions and an effective method and system for fast charging abattery.

In addition to the long recharge time, overheating or thermal runaway ofbattery, leading to a battery catching fire or battery explosion, hasbeen another serious barrier against the acceptance of battery-drivenEVs. There has been no effective approach to overcoming this batterysafety problem. An urgent need exists for a battery system that can beoperated in a safe mode free from any thermal runaway problem.

An object of the present disclosure is to provide a fast-chargeablebattery that can also operate in a safe mode with reduced or eliminatedchance of overheating, a method of operating same, and a system andapparatus for achieving both functions of fast chargeability andcooling.

SUMMARY

It may be noted that the word “electrode” herein refers to either ananode (negative electrode) or a cathode (positive electrode) of abattery. These definitions are also commonly accepted in the art ofbatteries or electrochemistry. In battery industry, a module comprises aplurality of battery cells packaged together. A pack comprises aplurality of modules aggregated together. The presently invented batterycharging system can be used to heat and charge one or a plurality ofbattery cells, regardless if or not they are packed into a module orpack or simply some individual battery cells. The term “battery” canrefer to a battery cell or several battery cells connected together.

In some embodiments, this disclosure provides a battery charging systemto enable fast charging of a battery (including one or multiple batterycells). The battery charging system comprises at least one chargingcircuit to charge at least one rechargeable battery cell and a heatsource to provide heat that is transported through a heat spreaderelement (implemented fully or partially inside the at least one batterycell) to heat up the battery cell or cells to a desired temperature Tcbefore or during conducting a fast charging operation of the batterycell(s). The battery charging system also comprises cooling means tocool down a battery cell or multiple battery cells in a module or packwhen the battery is discharged (e.g. when the cell(s) are operated topower an electronic device or EV motor). The heat generated inside acell is captured by the internally disposed heat spreader element, whichtransports the capture heat to the cooling means. The battery chargingsystem can operate alternately between a heating mode (when or beforethe battery cells are recharged) and a cooling mode (when the cells aredischarged).

In some preferred embodiments, the battery charging system comprisesmultiple charging stations to heat (and cool) and charge multiplerechargeable battery cells, wherein each charging station comprises onecharging circuit, one heat source, and cooling means.

The rechargeable battery cell preferably comprises an anode, a cathode,an electrolyte disposed between the anode and the cathode, a protectivehousing that at least partially encloses the anode, the cathode and theelectrolyte, at least one heat-spreader element disposed partially orentirely inside the protective housing and configured to receive heatfrom an external heat source at a desired heating temperature T_(h) toheat up the battery to a desired temperature Tc for battery charging. Insome embodiments, the heat-spreader element does not receive anelectrical current from an external circuit (e.g. battery charger) togenerate heat for resistance heating. Tc is typically chosen to be from30° C. to 90° C., more typically from 40° to 80° C., and most typicallyfrom 45° to 70° C.

A heat source may be heated by using laser heating, resistance heating,dielectric heating, thermal-electric heating, microwave heating, radiofrequency heating, hot fluid heating (e.g. hot water, steam, siliconeoil, etc. in a tubing), or a combination thereof.

The cooling means is preferably selected from a heat sink, a heat pipe,a vapor chamber, a stream of flowing fluid (when an EV is in motion, airmay be directed to flow into contact with the heat spreader tabs, forinstance), a thermoelectric device, a heat exchanger, a radiator, or acombination thereof.

Preferably, the heat-spreader element does not receive an electricalcurrent from the charging circuit to generate heat inside the batterycell for internal resistance heating of the battery cell (not producingJoule heat in situ inside the cell).

In some embodiments, the rechargeable battery cell further comprises atleast a temperature sensor for measuring an internal temperature of thebattery. In some embodiments, the heat-spreader element acts as atemperature sensor for measuring an internal temperature of the battery.For instance, the graphene sheet exhibits a resistance that varies withthe surrounding temperature and, as such, a simple resistancemeasurement may be used to indicate the local temperature where thegraphene sheet is disposed.

In certain embodiments, the heat-spreader element comprises a highthermal conductivity material having a thermal conductivity no less than10 W/mK. Preferably, the heat-spreader element comprises a materialselected from graphene film (e.g. composed of graphene sheets aggregatedtogether or bonded together into a film or sheet form), flexiblegraphite sheet, artificial graphite film (e.g. the films produced bycarbonizing and graphitizing a polymer film, such as polyimide), foil orsheet of Ag, Ag, Cu, Al, brass, steel, Ti, Ni, Mg alloy, siliconnitride, boron nitride, aluminum nitride, boron arsenide, a compositethereof, or a combination thereof.

The graphene film contains a graphene selected from pristine graphene,graphene oxide, reduced graphene oxide, graphene fluoride, graphenechloride, graphene bromide, graphene iodide, hydrogenated graphene,nitrogenated graphene, chemically functionalized graphene, or acombination thereof.

In certain embodiments, the heat-spreader element has a heat-spreadingarea at least as large as 50% of a surface area of the anode or cathode.The heat-spreader element is preferably flat and has a largeheat-spreading area having a length-to-thickness ratio greater than 10,preferably greater than 50, more preferably greater than 100, andfurther more preferably greater than 500. The heat-spreader elementtypically has a thickness from about 0.5 μm to about 1 mm.

In the battery charging system, the heat source preferably has aclipping means to reversibly grip or firmly connect with a tab of theheat spreader element.

Preferably, the heat-spreader element is in a heat-spreading relation tothe anode or the cathode and provides heat thereto before or duringcharging of the battery. For instance, the heat-spreader element isdisposed near or in physical contact with the anode or the cathode.There can be two or more heat spreader elements, one on the anode sideand the other on the cathode side

In certain embodiments, the heat-spreader element has a tab protrudedoutside of the protective housing, wherein the tab is configured tocontrollably make thermal contact with the external heat source (beforeor during battery charging) and get disconnected with the external heatsource when a battery temperature reaches the desired temperature Tc,for instance.

In certain embodiments, the battery cell has an anode terminal and acathode terminal for operating the battery and the heat-spreader elementis in thermal contact with the anode terminal or the cathode terminalwherein the anode terminal or the cathode terminal is configured toreceive heat from the outside heat source. In some configurations, theheat-spreader element is in thermal contact with the protective housingor a cap of the protective housing.

The rechargeable battery may be a lithium-ion battery, lithium metalsecondary battery, lithium-sulfur battery, lithium-air battery,lithium-selenium battery, sodium-ion battery, sodium metal secondarybattery, sodium-sulfur battery, sodium-air battery, magnesium-ionbattery, magnesium metal battery, aluminum-ion battery, aluminum metalsecondary battery, zinc-ion battery, zinc metal battery, zinc-airbattery, nickel metal hydride battery, lead acid battery, leadacid-carbon battery, lead acid-based ultra-battery, lithium-ioncapacitor, or supercapacitor.

The present disclosure also provides a method of operating a batterycharging system comprising multiple charging stations, the methodcomprising: (a) positioning multiple rechargeable battery cells in therespective multiple charging stations; (b) operating at least a heatsource of the battery charging system to provide heat that istransported through a heat spreader element (implemented fully orpartially inside each of said battery cells) to heat up the batterycells to a desired temperature Tc; and (c) activating at least onecharging circuit from the battery charging system to charge the batterycells at or near Tc until the battery cells reach a desired degree ofcharge (DOC).

In certain embodiments, preferably each of the battery cells comprisestherein a heat spreader element having an end connected to an electrodeterminal of the battery cell or having a tab protruded out of aprotective housing of the battery cell and wherein step (b) comprisesbringing the electrode terminal or the tab in thermal contact with anexternal heat source, allowing heat from the heat source to transferinto the battery cell for heating the battery to a desired temperatureTc.

In certain embodiments, the method further comprises a step of operatinga temperature sensor for measuring an internal temperature of thebattery. The step of operating a temperature sensor may compriseoperating the heat-spreader element as a temperature sensor formeasuring an internal temperature of the battery.

In the invented method, the heat-spreader element preferably comprises ahigh thermal conductivity material having a thermal conductivity no lessthan 10 W/mK and wherein a time for heating the battery to temperatureTc is no greater than 5 minutes.

In some preferred embodiments, the heat-spreader element comprises amaterial selected from graphene film, flexible graphite sheet,artificial graphite film, Ag, Ag, Cu, Al, brass, steel, Ti, Ni, Mg alloysheet, silicon nitride, boron nitride, aluminum nitride, boron arsenide,a composite thereof, or a combination thereof. The graphene filmpreferably contains a graphene selected from pristine graphene, grapheneoxide, reduced graphene oxide, graphene fluoride, graphene chloride,graphene bromide, graphene iodide, hydrogenated graphene, nitrogenatedgraphene, chemically functionalized graphene, or a combination thereof.

In some embodiments, the step of implementing a heat spreader elementinside the battery cell comprises placing the heat-spreader element inphysical or thermal contact with the anode or the cathode for providingheat thereto (e.g. for transporting heat through the anode or cathodeelectrode to heat up the battery prior to battery charging).

In some embodiments, the heat-spreader element has a tab protrudedoutside of the protective housing of a cell and step (b) comprisescontrollably making the tab to be in thermal contact with the externalheat source and disconnecting the tab from the external heat source whena battery temperature reaches the desired temperature Tc.

In certain embodiments, the heat-spreader element has a tab protrudedoutside of the protective housing and wherein (d) comprises controllablymaking the tab in thermal contact with the cooling means when thebattery cell is discharged.

In some embodiments, the battery cell has an anode terminal and acathode terminal for operating the battery cell and the heat-spreaderelement is in thermal contact with the anode terminal or the cathodeterminal and wherein step (b) comprises bringing the anode terminal orthe cathode terminal in physical or thermal contact with the externalheat source for battery charging; or wherein step (d) comprises bringingthe anode terminal or the cathode terminal in physical or thermalcontact with the cooling means when the battery cell is discharged.

In some embodiments, the heat-spreader element is in thermal contactwith the protective housing or a cap of the protective housing and step(b) comprises bringing the external heat source to thermally orphysically contact the protective housing or the cap, supplying heatthereto for cell charging; or said (d) comprises bringing the coolingmeans to thermally or physically contact the protective housing or thecap, removing heat therefrom for battery discharging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) Schematic of a battery according to an embodiment of thepresent disclosure; the heat spreader tab may be connected to a heatsource or, alternately, a heat sink.

FIG. 1(B) Schematic of a battery according to another embodiment of thepresent disclosure; the heat spreader tab (possibly connected to a cellcap or an electrode terminal) may be connected to a heat source or,alternately, a heat sink.

FIG. 2 A flow chart showing the method of operating the presentlyinvented battery charging and cooling system according to an embodimentof present disclosure.

FIG. 3(A) Schematic of a multiple-station battery charging and coolingsystem according to an embodiment of the present disclosure; eachstation providing a charging circuit (schematically represented by 2electric wires), a heat source (e.g. a heating element 56), and acooling means (not shown);

FIG. 3(B) Schematic of a multiple-station battery charging and coolingsystem according to another embodiment of the present disclosure; eachstation providing a charging circuit, a heat source (e.g. all 3 stationsdraw heat from the same heat source, a heated member 66 as an example),and a cooling means (e.g. a heat sink 68); FIG. 3(C) Schematic of amultiple-station battery charging system (for charging cylindricalcells, for instance) according to another embodiment of the presentdisclosure; each station providing a charging circuit (schematicallyrepresented by 2 electric wires), a heat source (e.g. a heatingelement), and a cooling means (not shown).

FIG. 4 Schematic of a heat spreader according to an embodiment of thepresent disclosure.

FIG. 5 Schematic of a battery pack charging and cooling system,according to an embodiment of the present disclosure. This battery packmay be disposed in the chassis of an electric vehicle.

FIG. 6 A diagram showing a procedure for producing graphene oxidesheets. These sheets can then be aggregated (e.g. roll-pressed) togetheror slurry-coated together, followed by a heat treatment procedure toproduce graphene films.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present discussion of preferred embodiments makes use of lithium-ionbattery as an example. The present disclosure is applicable to a widearray of rechargeable batteries, not limited to the lithium-ionbatteries. Examples of the rechargeable batteries include thelithium-ion battery, lithium metal secondary battery, lithium-sulfurbattery, lithium-air battery, lithium-selenium battery, sodium-ionbattery, sodium metal secondary battery, sodium-sulfur battery,sodium-air battery, magnesium-ion battery, magnesium metal battery,aluminum-ion battery, aluminum metal secondary battery, zinc-ionbattery, zinc metal battery, zinc-air battery, nickel metal hydridebattery, lead acid battery, lead acid-carbon battery, lead acid-basedultra-battery, lithium-ion capacitor, or supercapacitor

As indicated in the Background section of instant specification, lithiumplating on the anode material is a major obstacle to fast chargeabilityof a lithium-ion battery. A major symptom of lithium plating is adrastic capacity loss. Lithium plating can also pose safety hazards.Recent data available in battery industry has demonstrated that cyclelife of LiBs drops considerably with temperature. Typically, anexponential drop of cycle life with decreasing temperature is observed,following the Arrhenius law. For instance, even at a cool temperature of10° C., cell life is only about half of that at 25° C. Thus, even atfast charging stations, consumers are not able to quickly recharge theirEVs at low ambient temperatures. Compared to traditionalgasoline-powered vehicles whose fuel tank can be filled up in less thanfive minutes under all climate conditions, EV requires hours to get afull recharge in cold weather. Fast charging is essential to enablingpublic charge stations and battery-powered electric vehicles.

To avoid the danger of damaging the battery due to battery charging atlow ambient temperatures and to reduce the charging time, we propose toheat the rechargeable batteries to a near room-temperature range orhigher suitable for fast charging. However, conventional battery heatingsystems heat the battery externally by using convective air/liquidheating or thermal jackets, where heat slowly gets transported from theexterior into the battery. Such processes suffer from long heating timeand significant heat loss to the surroundings. Another conventionalapproach entails introducing electric current into the battery forinternal resistance heating of the battery. Such an approach runs thedanger of overheating the battery in that, when a large amount ofcurrent reaches an internal battery location in an extremely shortperiod of time, the resulting local hot spots can significantly degradeor damage the various component materials. Instant disclosure providesan effective solution to this problem.

In some embodiments, this disclosure provides a battery charging systemto enable fast charging of a battery. The battery charging systemcomprises at least one charging circuit to charge at least onerechargeable battery cell and a heat source to provide heat that istransported through a heat spreader element (implemented fully orpartially inside said at least one battery cell) to heat up said batterycell to a desired temperature Tc before or during conducting a fastcharging operation of the battery cell. The battery charging system alsohas a provision to cool the battery cells when the battery is discharged(e.g. when the battery is operated to power a load or external device).

Thus, the present disclosure also provides a battery charging systemcomprising (a) at least one charging circuit to charge at least onerechargeable battery cell; (b) at least a heat source to provide heatthat is transported through a heat spreader element (implemented fullyor partially inside said at least one battery cell) to heat up thebattery cell to a desired temperature Tc before or during charging ofthe battery cell; and (c) cooling means in thermal contact with the heatspreader element configured to enable transporting of internal heat ofthe battery cell through the heat spreader element to the cooling meanswhen the battery cell is discharged, wherein the cooling means is not inthermal contact with the heat spreader element when the battery cell isheated by the heat source.

In some embodiments, the rechargeable battery cell comprises an anode, acathode, an electrolyte disposed between the anode and the cathode, anda protective housing that at least partially encloses the anode, thecathode and the electrolyte, wherein the heat-spreader element isdisposed partially or entirely inside the protective housing andconfigured to alternate between receiving heat from the heat source at adesired heating temperature T_(h) to heat up the battery cell to thedesired temperature Tc for battery cell charging and transferring heatfrom the battery cell to the cooling means when the battery cell isdischarged or is operated to provide electric power to an externaldevice or load. Preferably, the heat-spreader element does not receivean electrical current from an external circuit (e.g. battery charger) togenerate heat for resistance heating.

As illustrated in FIG. 1(A), according to some embodiments of thedisclosure, the battery cell is in thermal or physical contact witheither an external heat source (e.g. a heating element or Peltierjunction heater, 22) before or during charging of the cell or,alternately, a cooling means (e.g. a heat sink 23, vapor chamber, orcooled plate) during cell discharging. The battery cell comprises ananode (negative electrode) 16, a cathode (positive electrode) 20, aseparator 18 and electrolyte (not shown) disposed between the anode andthe cathode, a casing or protective housing 12 that substantiallyencloses the above-listed components. Also enclosed is a heat spreaderelement 14, wherein the heat spreader element has a tab 24 protruded outof the battery cell housing 12. Also protruded out of the housing are anegative electrode terminal 26 connected to or integral with the anode16 and a positive electrode terminal 28 connected to or integral withthe cathode 20. The two electrode terminals are to be reversiblycontacted with a battery charger (during battery charging) or a load(e.g. an electronic device, such as a smart phone, to be powered by thebattery while discharging). It is the heat spreader element tab 24 thatis in thermal or physical contact with the external heat source thathelps to heat up the battery cell to a desired temperature for fastcharging.

As illustrated in FIG. 1(B), according to another embodiment of thedisclosure, the battery system comprises a battery cell in thermal orphysical contact with an external heat source (before or during batterycell charging) or, alternately, a cooling means (e.g. a heat sink)during battery discharging. The battery comprises an anode 36, a cathode40, a thin separator 38 and electrolyte (not shown) disposed between theanode and the cathode, a casing or protective housing 32 thatsubstantially encloses the above-listed components. Also enclosed is aheat spreader element 34, which has one end in thermal contact with ahousing cap (an example being shown in FIG. 3(C)); this cap, incombination with the housing 32, substantially seals the entire batterycell. This cap is, in turn, in thermal contact with the external heatsource or, alternately, cooling means. This cap may also serve as aterminal (e.g. negative terminal) for the battery cell; the positiveterminal being located at the opposite end of this cylindrical cell.Alternatively, this cap may serve as a positive terminal and theopposite end is a negative terminal.

As illustrated in FIG. 3(A), as an example, a battery charging andcooling system can contain multiple charging stations for chargingmultiple battery cells (e.g. in a module or a pack). Each chargingstation comprises a charging circuit to charge a battery cell (e.g. 50)and a heat source (e.g. a heating element 56) to provide heat that istransferred though a heat spreader element 52 implemented inside abattery cell to heat up the cell for fast charging. Each cell has atleast a heat spreader element (disposed partially or entirely inside thebattery cell) that is in thermal contact with at least an external heatsource 56 through a tab 54 of the heat spreader element 52 before orduring battery cell charging. The battery charging and cooling systemalso contains cooling means that can alternately replace the heat sourceto be in thermal contact with the tab of the heat spreader when thebattery is discharged.

As illustrated in FIG. 3(B), one heat source 66 may be in thermalcontact with one or a plurality of heat spreader elements (e.g. thoseheat spreader elements in multiple cells). Although FIG. 3(A), as anexample, shows three heat sources that are connected to three batterycells, these three heat sources can be just from the same heating means.For instance, the same heated plate (e.g. 66 in FIG. 3(B)) can be usedto heat three or more battery cells by heat conductance through theirrespective heat spreader elements into the individual cells. When thebattery cell is discharged, those heat spreader elements are in thermalcontact with cooling means (e.g. heat sink 68). FIG. 3(C) schematicallyshows a multiple-station battery charging/cooling system (forcharging/cooling cylindrical cells, for instance) according to anotherembodiment of the present disclosure; each station providing a chargingcircuit (schematically represented by 2 electric wires), a heat source(e.g. a heating element), and a cooling means (not shown).

Schematically shown in FIG. 5 is a battery pack charging/cooling system,according to an embodiment of the present disclosure. This battery packmay be disposed in the chassis of an electric vehicle. In additional toa battery charging circuit that can recharge all the battery cells inthis pack, there are thermal circuits that provide heat to enter thecells through their respective heat spreader elements. These thermalcircuits may include electrical circuits that send electric power toheating devices near individual battery cells. These thermal circuitsmay be simply some heated members that are strategically positioned withrespect to individual battery cells to readily transfer heat through theheat spreader tabs or cell caps into the cells. When the battery cellsin the pack are discharged to drive the EV, the thermal circuits maybecome cooling means to keep the battery lower than a safe temperature.

There is no limitation on the type and nature of the external heatsource provided that this heat source per se is capable of providingheat to the heat spreader element without sending an electrical currentthrough this element into the battery cell for internal joule heating ofthe battery cell. For instance, the external heat source may be assimple as a metal plate or a metal clip that is already at a desiredheating temperature T_(h) prior to being brought to contact the element.Such an arrangement of having a ready-to-heat heat source, inconjunction with a heat spreader element of high thermal conductivity,will significantly reduce the time to bring a battery cell to a desiredtemperature for fast charging.

Alternatively, the external heat source may be rapidly heated to reachT_(h) as soon as the heat spreader element is brought in contact withthe external heat source. This heat source may be heated by using anyknown heating means; e.g. laser heating, resistance heating, dielectricheating, thermal-electric heating (e.g. Peltier junction heating),microwave heating, radio frequency (RF) heating, etc. Any of theseheating means may be used to directly heat the external tab of the heatspreader element provided it does not send a current into the battery.One or a plurality of external heat sources may be used to provide heatto one or a plurality of heat spreader elements of one or a plurality ofbatteries concurrently or sequentially.

There is also no limitation on the type of cooling means that can beimplemented to cool down the battery cells when working to power anelectronic device or an EV. The cooling means may be selected from aheat sink, a heat pipe, a vapor chamber, a stream of flowing fluid, athermoelectric device, a heat exchanger, a radiator, or a combinationthereof.

It is important that the heat spreader element has a high thermalconductivity to allow for rapid transfer of a large amount of heat fromthe external heat source through the heat spreader element to theinterior of the battery to be recharged. Such a heat spreader elementalso enables fast heat transfer from the interior of a battery cell tothe cooling means (external to the battery cell) when the cell isdischarged. Preferably, for fast charging of the battery cell, such ahigh thermal conductivity and the cross-sectional area of the heatspreader element are sufficiently high to ensure the battery reaching adesired temperature in less than 15 minutes (preferably less than 10minutes, further preferably less than 5 minutes, most preferably lessthan 2 minutes) to enable fast charging. After charging begins,preferably charging is completed in 15 minutes (4 C rate), preferably in10 minutes (6 C rate), further preferably in 5 minutes (12 C rate), andmost preferably in 2 minutes (30 C rate). The battery charging C rate isdefined as follows: a nC rate means completion of charging in 60/nminutes or 1/n hour; a 3 C rate means completing the charging in 60/3=20minutes and a C/3 rate means completing charging in 3 hours.

In certain embodiments, the heat-spreader element comprises a highthermal conductivity material having a thermal conductivity no less than10 W/mK (preferably no less than 20 W/mK, further preferably greaterthan 200 W/mK, more preferably greater than 400 W/mK, and mostpreferably greater than 800 W/mK). Preferably, the heat-spreader elementcomprises a material selected from graphene film (e.g. composed ofgraphene sheets aggregated together or bonded together into a film orsheet form), flexible graphite sheet, artificial graphite film (e.g. thefilms produced by carbonizing and graphitizing a polymer film, such aspolyimide), foil or sheet of Ag, Ag, Cu, Al, brass, steel, Ti, Ni, Mgalloy, silicon nitride, boron nitride, aluminum nitride, boron arsenide,a composite thereof, or a combination thereof.

The graphene film contains a graphene selected from pristine graphene,graphene oxide, reduced graphene oxide, graphene fluoride, graphenechloride, graphene bromide, graphene iodide, hydrogenated graphene,nitrogenated graphene, chemically functionalized graphene, or acombination thereof. The graphene film typically exhibits a thermalconductivity from 800 to 1,800 W/mK. Flexible graphite sheet typicallyexhibits a thermal conductivity from 150 to 600 W/mK. Artificialgraphite films (e.g. those produced by carbonizing and graphitizing apolymer film) can exhibit a thermal conductivity from 600 to 1,700 W/mK.Graphene films, flexible graphite sheets, and artificial graphite filmsare commonly regarded as three distinct classes of materials.

In some embodiments, the rechargeable battery further comprises at leasta temperature sensor for measuring an internal temperature of thebattery. In some embodiments, the heat-spreader element acts as atemperature sensor for measuring an internal temperature of the battery.For instance, the graphene sheet exhibits a resistance that varies withthe surrounding temperature and, as such, a simple resistancemeasurement may be used to indicate the local temperature where thegraphene sheet is disposed.

Carbon materials can assume an essentially amorphous structure (glassycarbon), a highly organized crystal (graphite), or a whole range ofintermediate structures that are characterized in that variousproportions and sizes of graphite crystallites and defects are dispersedin an amorphous matrix. Typically, a graphite crystallite is composed ofa number of graphene sheets or basal planes that are bonded togetherthrough van der Waals forces in the c-axis direction, the directionperpendicular to the basal plane. These graphite crystallites aretypically micron- or nanometer-sized. The graphite crystallites aredispersed in or connected by crystal defects or an amorphous phase in agraphite particle, which can be a graphite flake, carbon/graphite fibersegment, carbon/graphite whisker, or carbon/graphite nano-fiber. Inother words, graphene planes (hexagonal lattice structure of carbonatoms) constitute a significant portion of a graphite particle.

A single-layer graphene sheet is composed of carbon atoms occupying atwo-dimensional hexagonal lattice. Multi-layer graphene is a plateletcomposed of more than one graphene plane. Individual single-layergraphene sheets and multi-layer graphene platelets are hereincollectively called nano graphene platelets (NGPs) or graphenematerials. NGPs include pristine graphene (essentially 99% of carbonatoms), slightly oxidized graphene (<5% by weight of oxygen), grapheneoxide (≥5% by weight of oxygen), slightly fluorinated graphene (<5% byweight of fluorine), graphene fluoride ((≥5% by weight of fluorine),other halogenated graphene, and chemically functionalized graphene.

Our research group was among the first to discover graphene [B. Z. Jangand W. C. Huang, “Nano-scaled Graphene Plates,” U.S. patent applicationSer. No. 10/274,473, submitted on Oct. 21, 2002; now U.S. Pat. No.7,071,258 (Jul. 4, 2006)]. The processes for producing NGPs and NGPnanocomposites were recently reviewed by us [Bor Z. Jang and A Zhamu,“Processing of Nano Graphene Platelets (NGPs) and NGP Nanocomposites: AReview,” J. Materials Sci. 43 (2008) 5092-5101]. The production ofvarious types of graphene sheets is well-known in the art.

For instance, as shown in FIG. 6, the chemical processes for producinggraphene sheets or platelets typically involve immersing powder ofgraphite or other graphitic material in a mixture of concentratedsulfuric acid, nitric acid, and an oxidizer, such as potassiumpermanganate or sodium perchlorate, forming a reacting mass thatrequires typically 5-120 hours to complete the chemicalintercalation/oxidation reaction. Once the reaction is completed, theslurry is subjected to repeated steps of rinsing and washing with water.The purified product is commonly referred to as graphite intercalationcompound (GIC) or graphite oxide (GO). The suspension containing GIC orGO in water may be subjected to ultrasonication to produceisolated/separated graphene oxide sheets dispersed in water. Theresulting products are typically highly oxidized graphene (i.e. grapheneoxide with a high oxygen content), which must be chemically or thermalreduced to obtain reduced graphene oxide (RGO).

Alternatively, the GIC suspension may be subjected to drying treatmentsto remove water. The dried powder is then subjected to a thermal shocktreatment. This can be accomplished by placing GIC in a furnace pre-setat a temperature of typically 800-1100° C. (more typically 950-1050° C.)to produce exfoliated graphite (or graphite worms), which may besubjected to a high shear or ultrasonication treatment to produceisolated graphene sheets.

Alternatively, graphite worms may be re-compressed into a film form toobtain a flexible graphite sheet. Flexible graphite sheets arecommercially available from many sources worldwide.

The starting graphitic material may be selected from natural graphite,synthetic graphite, highly oriented pyrolytic graphite, graphite fiber,graphitic nano-fiber, graphite fluoride, chemically modified graphite,meso-carbon micro-bead, partially crystalline graphite, or a combinationthereof.

Pristine graphene sheets may be produced by the well-known liquid phaseexfoliation or metal-catalyzed chemical vapor deposition (CVD).

The heat-spreader element preferably has a heat-spreading area at leastas large as 50% of a surface area of the anode or cathode. Theheat-spreader element is preferably flat and has a large heat-spreadingarea having a length-to-thickness ratio greater than 10, preferablygreater than 50, more preferably greater than 100, and further morepreferably greater than 500. The heat-spreader element typically has athickness from about 0.5 μm to about 1 mm.

Preferably, the heat-spreader element is in a heat-spreading relation tothe anode or the cathode and provides heat thereto before or duringcharging of the battery. For instance, the heat-spreader element isdisposed near or in physical contact with the anode or the cathodeinside the battery. There can be two heat spreader elements, one on theanode side and the other on the cathode side of a cell.

Preferably, as schematically illustrated in FIG. 1(A), the heat-spreaderelement has a tab protruded outside of the protective housing of a cell,wherein the tab is configured to controllably make thermal contact withthe external heat source (before or during battery charging) and getdisconnected with the external heat source when a battery celltemperature reaches the desired temperature Tc, for instance. Thebattery cell has an anode terminal and a cathode terminal that areconnected to an anode circuit and cathode circuit, respectively, foroperating the battery (e.g. for battery charging and discharging).During discharging of the battery cell (e.g. providing power to a smartphone or an EV), these two terminals are connected to the properterminals of the battery management system (BMS) of the smart phone orEV. During the charging of the battery, these two terminals may bedirectly connected to an external battery charger or indirectly througha BMS to an external battery charger. The battery charger and BMS arewell-known in the art.

In certain embodiments, the battery cell has an anode terminal and acathode terminal for operating the battery and the heat-spreader elementis in thermal contact with the anode terminal or the cathode terminalwherein the anode terminal or the cathode terminal is configured toreceive heat from the outside heat source. In some configurations, asillustrated in FIG. 1(B), the heat-spreader element is in thermalcontact with the protective housing or a cap of the protective housingof a cell. This cap or housing may be made to contact with an externalheat source to receive heat therefrom. Shown in FIG. 1(B) is but one ofmany possible configurations, wherein a sheet of heat spreader (e.g.graphene film) is disposed inside a casing (protective housing) to wraparound the anode. One end of the heat spreader element is in contactwith the battery cap, which may receive heat from an external heatsource (when the cap is in contact with the heat source).

The rechargeable battery may be a lithium-ion battery, lithium metalsecondary battery, lithium-sulfur battery, lithium-air battery,lithium-selenium battery, sodium-ion battery, sodium metal secondarybattery, sodium-sulfur battery, sodium-air battery, magnesium-ionbattery, magnesium metal battery, aluminum-ion battery, aluminum metalsecondary battery, zinc-ion battery, zinc metal battery, zinc-airbattery, nickel metal hydride battery, lead acid battery, leadacid-carbon battery, lead acid-based ultra-battery, lithium-ioncapacitor, or supercapacitor.

There is no limitation on the type of anode materials, electrolytes,cathode materials, etc. that can be used in the presently inventedbattery.

The anode of a lithium-ion battery (as an example) may contain an anodeactive material selected from the group consisting of: (A) lithiated andun-lithiated silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony(Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel(Ni), cobalt (Co), phosphorus (P), and cadmium (Cd); (B) lithiated andun-lithiated alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb,Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements; (C) lithiated andun-lithiated oxides, carbides, nitrides, sulfides, phosphides,selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni,Co, or Cd, and their mixtures, composites, or lithium-containingcomposites; (D) lithiated and un-lithiated salts and hydroxides of Sn;(E) lithium titanate, lithium manganate, lithium aluminate,lithium-containing titanium oxide, lithium titanium-niobium oxide,lithium transition metal oxide; (F) carbon or graphite particles; andcombinations thereof.

The cathode may contain a cathode active material selected from aninorganic material, an organic material, an intrinsically conductingpolymer (known to be capable of string lithium ions), a metaloxide/phosphate/sulfide, or a combination thereof. The metaloxide/phosphate/sulfide may be selected from a lithium cobalt oxide,lithium nickel oxide, lithium manganese oxide, lithium vanadium oxide,lithium-mixed metal oxide, lithium iron phosphate, lithium manganesephosphate, lithium vanadium phosphate, lithium mixed metal phosphate,sodium cobalt oxide sodium nickel oxide, sodium manganese oxide, sodiumvanadium oxide, sodium-mixed metal oxide, sodium iron phosphate, sodiummanganese phosphate, sodium vanadium phosphate, sodium mixed metalphosphate, transition metal sulfide, lithium polysulfide, sodiumpolysulfide, magnesium polysulfide, or a combination thereof.

In some embodiments, the electrode active material may be a cathodeactive material selected from sulfur, sulfur compound, sulfur-carboncomposite, sulfur-polymer composite, lithium polysulfide, transitionmetal dichalcogenide, a transition metal trichalcogenide, or acombination thereof. The inorganic material may be selected from TiS₂,TaS₂, MoS₂, NbSe₃, MnO₂, CoO₂, an iron oxide, a vanadium oxide, or acombination thereof. This group of materials is particularly suitablefor use as a cathode active material of a lithium metal battery.

The metal oxide/phosphate/sulfide contains a vanadium oxide selectedfrom the group consisting of VO₂, LiVO₂, V₂O₅, Li_(x)V₂O₅, V₃O₈,Li_(x)V₃O₈, Li_(x)V₃O₇, V₄O₉, Li_(x)V₄O₉, V₆O₁₃, Li_(x)V₆O₁₃, theirdoped versions, their derivatives, and combinations thereof, wherein 0.1<x <5. In some embodiments, the metal oxide/phosphate/sulfide isselected from a layered compound LiMO₂, spinel compound LiM₂O₄, olivinecompound LiMPO₄, silicate compound Li₂MSiO₄, Tavorite compound LiMPO₄F,borate compound LiMBO₃, or a combination thereof, wherein M is atransition metal or a mixture of multiple transition metals.

The inorganic material may be selected from: (a) bismuth selenide orbismuth telluride, (b) transition metal dichalcogenide ortrichalcogenide, (c) sulfide, selenide, or telluride of niobium,zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt,manganese, iron, nickel, or a transition metal; (d) boron nitride, or(e) a combination thereof.

The organic material or polymeric material may be selected frompoly(anthraquinonyl sulfide) (PAQS), a lithium oxocarbon,3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA),poly(anthraquinonyl sulfide), pyrene-4,5,9,10-tetraone (PYT),polymer-bound PYT, quino(triazene), redox-active organic material,tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE),2,3,6,7,10,11-hexamethoxytriphenylene (HMTP), poly(5-amino-1,4-dyhydroxyanthraquinone) (PADAQ), phosphazene disulfide polymer ([(NPS₂)₃]n),lithiated 1,4,5,8-naphthalenetetraol formaldehyde polymer,hexaazatrinaphtylene (HATN), hexaazatriphenylene hexacarbonitrile(HAT(CN)₆), 5-benzylidene hydantoin, isatine lithium salt, pyromelliticdiimide lithium salt, tetrahydroxy-p-benzoquinone derivatives (THQLi₄),N,N′-diphenyl-2,3,5,6-tetraketopiperazine (PHP),N,N′-diallyl-2,3,5,6-tetraketopiperazine (AP),N,N′-dipropyl-2,3,5,6-tetraketopiperazine (PRP), a thioether polymer, aquinone compound, 1,4-benzoquinone, 5,7,12,14-pentacenetetrone (PT),5-amino-2,3-dihydro-1,4-dyhydroxy anthraquinone (ADDAQ),5-amino-1,4-dyhydroxy anthraquinone (ADAM), calixquinone, Li₄C₆O₆,Li₂C₆O₆, Li₆C₆O₆, or a combination thereof. These compounds arepreferably mixed with a conducting material to improve their electricalconductivity, rigidity and strength so as to enable the peeling-off ofgraphene sheets from the graphitic material particles.

The thioether polymer in the above list may be selected frompoly[methanetetryl-tetra(thiomethylene)] (PMTTM),poly(2,4-dithiopentanylene) (PDTP), a polymer containingpoly(ethene-1,1,2,2-tetrathiol) (PETT) as a main-chain thioetherpolymers, a side-chain thioether polymer having a main-chain consistingof conjugating aromatic moieties, and having a thioether side chain as apendant, poly(2-phenyl-1,3-dithiolane) (PPDT),poly(l,4-di(1,3-dithiolan-2-yl)benzene) (PDDTB),poly(tetrahydrobenzodithiophene) (PTHBDT),poly[1,2,4,5-tetrakis(propylthio)benzene] (PTKPTB, or poly[3,4(ethylenedithio)thiophene] (PEDTT).

In some embodiments, the organic material contains a phthalocyaninecompound selected from copper phthalocyanine, zinc phthalocyanine, tinphthalocyanine, iron phthalocyanine, lead phthalocyanine, nickelphthalocyanine, vanadyl phthalocyanine, fluorochromium phthalocyanine,magnesium phthalocyanine, manganous phthalocyanine, dilithiumphthalocyanine, aluminum phthalocyanine chloride, cadmiumphthalocyanine, chlorogallium phthalocyanine, cobalt phthalocyanine,silver phthalocyanine, a metal-free phthalocyanine, a chemicalderivative thereof, or a combination thereof. These compounds arepreferably mixed with a conducting material to improve their electricalconductivity and rigidity so as to enable the peeling-off of graphenesheets from the graphitic material particles.

There is no limitation on the type of electrolyte that can beincorporated in the fast-chargeable battery: liquid electrolyte (e.g.organic solvent or ionic solid based electrolyte), polymer gelelectrolyte, quasi-solid electrolyte, solid polymer electrolyte,inorganic solid electrolyte, composite electrolyte, etc. Batteriesfeaturing a polymer or inorganic solid electrolyte may require a higherrecharge temperature, having Tc typically from 50 to 90° C.

The present disclosure also provides a method of operating a batterycharging/cooling system comprising multiple charging stations. Asillustrated in FIG. 2 as an example, the method comprising: (a)positioning multiple rechargeable battery cells in the respectivemultiple charging stations; (b) operating at least a heat source of thebattery charging system to provide heat that is transported through aheat spreader element (implemented fully or partially inside each ofsaid battery cells) to heat up the battery cells to a desiredtemperature Tc; and (c) activating at least one charging circuit fromthe battery charging system to charge the battery cells at or near Tcuntil the battery cells reach a desired degree of charge (DOC).

In certain embodiments, preferably each of the battery cells comprisestherein a heat spreader element having an end connected to an electrodeterminal of the battery cell or having a tab protruded out of aprotective housing of the battery cell and wherein step (b) comprisesbringing the electrode terminal or the tab in thermal contact with anexternal heat source (e.g. if the battery is at a temperature lower thana desired charging temperature, Tc), allowing heat from the heat sourceto transfer into the battery cell for heating the battery to a desiredtemperature Tc.

In certain embodiments, the method further comprises a step of operatinga temperature sensor for measuring an internal temperature of thebattery. The step of operating a temperature sensor may compriseoperating the heat-spreader element as a temperature sensor formeasuring an internal temperature of the battery cell.

In the invented method, the heat-spreader element preferably comprises ahigh thermal conductivity material having a thermal conductivity no lessthan 10 W/mK (preferably no less than 20 W/mK, further preferablygreater than 200 W/mK, more preferably greater than 400 W/mK, and mostpreferably greater than 800 W/mK), and wherein a time for heating thebattery to temperature Tc is preferably no greater than 15 minutes(preferably less than 10 minutes, further preferably less than 5minutes, most preferably less than 2 minutes).

In some preferred embodiments, the heat-spreader element comprises amaterial selected from graphene film, flexible graphite sheet,artificial graphite film, Ag, Ag, Cu, Al, brass, steel, Ti, Ni, Mg alloysheet, silicon nitride, boron nitride, aluminum nitride, boron arsenide,a composite thereof, or a combination thereof. The graphene filmpreferably contains a graphene selected from pristine graphene, grapheneoxide, reduced graphene oxide, graphene fluoride, graphene chloride,graphene bromide, graphene iodide, hydrogenated graphene, nitrogenatedgraphene, chemically functionalized graphene, or a combination thereof.

In some embodiments, the step of implementing a heat spreader elementinside the battery cell comprises placing the heat-spreader element inphysical or thermal contact with the anode or the cathode for providingheat thereto (e.g. for transporting heat through the anode or cathodeelectrode to heat up the battery cell prior to battery charging).

In some embodiments, the heat-spreader element has a tab protrudedoutside of the protective housing (e.g. as illustrated in FIG. 1(A)) andstep (b) comprises controllably making the tab to be in thermal contactwith the external heat source and disconnecting the tab from theexternal heat source when a battery temperature reaches the desiredtemperature Tc.

In certain embodiments, the heat-spreader element has a tab protrudedoutside of the protective housing and wherein (d) comprises controllablymaking the tab in thermal contact with the cooling means when thebattery cell is discharged.

In some embodiments, the battery cell has an anode terminal and acathode terminal for operating the battery cell and the heat-spreaderelement is in thermal contact with the anode terminal or the cathodeterminal and wherein step (b) comprises bringing the anode terminal orthe cathode terminal in physical or thermal contact with the externalheat source for battery charging; or wherein step (d) comprises bringingthe anode terminal or the cathode terminal in physical or thermalcontact with the cooling means when the battery cell is discharged.

In some embodiments, the heat-spreader element is in thermal contactwith the protective housing or a cap of the protective housing and step(b) comprises bringing the external heat source to thermally orphysically contact the protective housing or the cap, supplying heatthereto for cell charging; or said (d) comprises bringing the coolingmeans to thermally or physically contact the protective housing or thecap, removing heat therefrom for battery discharging.

In certain desired embodiments, the battery cell has an anode terminaland a cathode terminal for operating the battery cell and theheat-spreader element is in thermal contact with the anode terminal orthe cathode terminal (e.g. the cathode terminal protruded out as abattery cell cap of FIG. 1(B) and a graphene film is configured to be inthermal contact with this cap), wherein step (b) comprises bringing anelectrode terminal (e.g. the cathode terminal) in physical or thermalcontact with the external heat source. In some embodiments, theheat-spreader element is in thermal contact with the protective housingor a cap of the protective housing and step (b) comprises bringing theexternal heat source to thermally or physically contact the protectivehousing or the cap, supplying heat thereto.

FIG. 4 shows a heat spreader in which the height, length, and thicknessdimensions are defined. It should be understood that this drawing is notto scale, and is drawn in a manner to ease understanding, as thethickness may be much smaller (in a relative sense) than is shown. Alsoshown is an external heat source or means of cooling (or component of aheat source or means of cooling) that can be controllably moved into andout of thermal contact with the external tab of the heat source (asindicated by the double-headed arrow of FIG. 4). Lastly, a temperaturesensor is shown which can be on the surface of the heat spreader,internal to the battery but spaced-apart from the heat spreader, or anyother suitable location. It may be a resistive sensor, where theresistance is indicative of the temperature of the heat spreader or ofthe battery.

The following examples serve to provide the best modes of practice forthe present disclosure and should not be construed as limiting the scopeof the disclosure:

EXAMPLE 1 Preparation of Single-Layer Graphene Sheets and TheirHeat-Spreader Films from Meso-Carbon Micro-Beads (MCMBs)

Meso-carbon microbeads (MCMBs) were supplied from China Steel ChemicalCo., Kaohsiung, Taiwan. This material has a density of about 2.24 g/cm³with a median particle size of about 16 μm. MCMB (10 grams) wereintercalated with an acid solution (sulfuric acid, nitric acid, andpotassium permanganate at a ratio of 4:1:0.05) for 48-96 hours. Uponcompletion of the reaction, the mixture was poured into deionized waterand filtered. The intercalated MCMBs were repeatedly washed in a 5%solution of HC1 to remove most of the sulphate ions. The sample was thenwashed repeatedly with deionized water until the pH of the filtrate wasno less than 4.5. The slurry was then subjected ultrasonication for10-100 minutes to produce GO suspensions. TEM and atomic forcemicroscopic studies indicate that most of the GO sheets weresingle-layer graphene when the oxidation treatment exceeded 72 hours,and 2- or 3-layer graphene when the oxidation time was from 48 to 72hours.

The GO sheets contain oxygen proportion of approximately 35%-47% byweight for oxidation treatment times of 48-96 hours. GO sheets weresuspended in water. The GO suspension was cast into thin graphene oxidefilms on a glass surface and, separately, was also slot die-coated ontoa PET film substrate, dried, and peeled off from the PET substrate toform GO films. The GO films were separately heated from room temperatureto 2,500° C. and then roll-pressed to obtain reduced graphene oxide(RGO) films for use as a heat spreader. The thermal conductivity ofthese films were found to be from 1,225 to 1,750 W/mK using Neize heatconductivity measuring device.

EXAMPLE 2 Preparation of Pristine Graphene Sheets (0% Oxygen) and HeatSpreader Films

Pristine graphene sheets were produced by using the directultrasonication or liquid-phase production process. In a typicalprocedure, five grams of graphite flakes, ground to approximately 20 μmor less in sizes, were dispersed in 1,000 mL of deionized water(containing 0.1% by weight of a dispersing agent, Zonyl® FSO fromDuPont) to obtain a suspension. An ultrasonic energy level of 85 W(Branson 5450 Ultrasonicator) was used for exfoliation, separation, andsize reduction of graphene sheets for a period of 15 minutes to 2 hours.The resulting graphene sheets are pristine graphene that have never beenoxidized and are oxygen-free and relatively defect-free. There are noother non-carbon elements.

The pristine graphene sheets were immersed into a 10 mM acetone solutionof BPO for 30 min and were then taken out drying naturally in air. Theheat-initiated chemical reaction to functionalize graphene sheets wasconducted at 80° C. in a high-pressure stainless steel container filledwith pure nitrogen. Subsequently, the samples were rinsed thoroughly inacetone to remove BPO residues for subsequent Raman characterization. Asthe reaction time increased, the characteristic disorder-induced D bandaround 1330 cm⁻¹ emerged and gradually became the most prominent featureof the Raman spectra. The D-band is originated from the A_(ig) modebreathing vibrations of six-membered sp² carbon rings, and becomes Ramanactive after neighboring sp² carbon atoms are converted to sp³hybridization. In addition, the double resonance 2D band around 2670cm⁻¹ became significantly weakened, while the G band around 1580 cm⁻¹was broadened due to the presence of a defect-induced D′ shoulder peakat ˜1620 cm⁻¹. These observations suggest that covalent C—C bonds wereformed and thus a degree of structural disorder was generated by thetransformation from sp² to sp³ configuration due to reaction with BPO.

The functionalized graphene sheets were re-dispersed in water to producea graphene dispersion. The dispersion was then made into graphene filmsusing comma coating and subjected to heat treatments up to 2,500° C. Theheat spreader films obtained from functionalized graphene sheets exhibita thermal conductivity from 1,450 to 1,750 W/mK. On a separate basis,non-functionalized pristine graphene powder was directly compressed intographene films (aggregates of graphene sheets) using pairs of steelrollers; no subsequent heat treatment was conducted. These graphenefilms exhibit a thermal conductivity typically from approximately 600 toabout 1,000 W/mK.

EXAMPLE 3 Preparation of Graphene Fluoride Sheets and Heat SpreaderFilms

Several processes have been used by us to produce GF, but only oneprocess is herein described as an example. In a typical procedure,highly exfoliated graphite (HEG) was prepared from intercalated compoundC₂F.xClF₃. HEG was further fluorinated by vapors of chlorine trifluorideto yield fluorinated highly exfoliated graphite (FHEG). Pre-cooledTeflon reactor was filled with 20-30 mL of liquid pre-cooled ClF₃, thereactor was closed and cooled to liquid nitrogen temperature. Then, nomore than 1 g of HEG was put in a container with holes for ClF₃ gas toaccess and situated inside the reactor. In 7-10 days a gray-beigeproduct with approximate formula C₂F was formed.

Subsequently, a small amount of FHEG (approximately 0.5 mg) was mixedwith 20-30 mL of an organic solvent (methanol, ethanol, 1-propanol,2-propanol, 1-butanol, tert-butanol, isoamyl alcohol) and subjected toan ultrasound treatment (280 W) for 30 min, leading to the formation ofhomogeneous yellowish dispersions. Five minutes of sonication was enoughto obtain a relatively homogenous dispersion, but a longer sonicationtime ensured better stability. Upon extrusion to form wet films on aglass surface with the solvent removed, the dispersion became brownishfilms formed on the glass surface. The dried films, upon drying androll-pressing, became heat spreader films having a reasonably goodthermal conductor (thermal conductivity from 250 to 750 W/mK), yet anelectrical insulator. The unique combination of electrical insulationand thermal conduction characteristics is of particular interest forbattery heating configurations wherein there is no concern of anypotential negative effect cause by an electrical conductor.

EXAMPLE 4 Preparation of Nitrogenated Graphene Sheets and Graphene Filmsfor Use as a Heat Spreader Element

Graphene oxide (GO), synthesized in Example 1, was finely ground withdifferent proportions of urea and the pelletized mixture heated in amicrowave reactor (900 W) for 30 s. The product was washed several timeswith deionized water and vacuum dried. In this method graphene oxidegets simultaneously reduced and doped with nitrogen. The productsobtained with graphene/urea mass ratios of 1/0.5, 1/1 and 1/2 have thenitrogen contents of 14.7, 18.2 and 17.5 wt. %, respectively, as foundby elemental analysis. These nitrogenated graphene sheets, without priorchemical functionalization, remain dispersible in water. The resultingsuspensions were then coated and made into wet films and then dried. Thedried films were roll-pressed to obtain graphene films, having a thermalconductivity from 350 to 820 W/mK. These films are also electricalinsulators.

EXAMPLE 5 Fast-Chargeable Lithium-Ion, Sodium-Ion, Lithium Metal,Lithium-Sulfur Batteries Enabled by Heat-Spreader Heating

For most of the anode and cathode active materials investigated, weprepared lithium-ion cells or lithium metal cells using the conventionalslurry coating method. A typical anode composition includes 85 wt. %active material (e.g., graphene-encapsulated Si, SiO, SnO₂, and Co₃O₄particles available from Angstron Energy Co., Dayton, Ohio), 7 wt. %acetylene black (Super-P), and 8 wt. % polyvinylidene fluoride binder(PVDF, 5 wt. % solid content) dissolved in N-methyl-2-pyrrolidinoe(NMP). After coating the slurries on Cu foil, the electrodes were driedat 120° C. in vacuum for 2 h to remove the solvent. It may be noted thatCu foil recited here is used as a current collector that allows electriccurrent to go in and out of the anode electrode. A separate sheet of Cufoil may be added as a heat spreader element for heat-transportingpurpose, not for conducting electrons.

Cathode layers (e.g. LFP, NCM, LiCoO₂, etc.) are made in a similarmanner (using Al foil as the cathode current collector) using theconventional slurry coating and drying procedures.

An anode layer, separator layer (e.g. Celgard 2400 membrane), a cathodelayer, and a heat spreader layer (graphene film, flexible graphitesheet, Cu foil, Ni foil, etc.) are then laminated together and housed ina plastic-Al envelop (a protective housing or casing). An anode tab orterminal, a cathode tab, and a heat spreader tab are allowed to getprotruded out of the protective housing, as illustrated in FIG. 1(A).

The cell is then injected with 1 M LiPF₆ electrolyte solution dissolvedin a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC)(EC-DEC, 1:1 v/v). In some cells, ionic liquids were used as the liquidelectrolyte. The cell assemblies were made in an argon-filled glove-box.

The cyclic voltammetry (CV) measurements were carried out using an Arbinelectrochemical workstation at a typical scanning rate of 1-100 mV/s. Inaddition, the electrochemical performances of various cells were alsoevaluated by galvanostatic charge/discharge cycling at a current densityof from 50 mA/g to 10 A/g. For long-term cycling tests, multi-channelbattery testers manufactured by LAND were used. Anenvironment-controlled oven was used to perform battery testing atdifferent temperatures when desired.

EXAMPLE 6 Some Examples of Cathode Active Materials for a Lithium MetalBattery

Cathode active materials in lithium-ion or lithium metal secondarybatteries are known to have a relatively low thermal conductivity. It isthus advantageous to encapsulate cathode active material particles withgraphene which, if coupled with a high thermal conductivity heatspreader (e.g. graphene film or artificial graphite film fromgraphitized PI), enables faster heating of the battery to a desiredtemperature for fast charging.

For instance, lithium iron phosphate (LFP) powder, un-coated orcarbon-coated, is commercially available from several sources. Thecarbon-coated LFP powder and un-coated LFP powder samples wereseparately mixed with natural graphite particles in ball mill pots of ahigh-intensity ball mill apparatus. The apparatus was operated for 0.5to 4 hours for each LFP material to produce graphene-encapsulated LFPparticles.

V₂O₅ powder is commercially available. A mixture of V₂O₅ powder andnatural graphite (10/1 weight ratio) was sealed in each of 4 ballmilling pots symmetrically positioned in a high-intensity ball mill. Themill was operated for 1 hour to produce particulates ofgraphene-encapsulated V₂O₅ particles, which were implemented as thecathode active material in a lithium metal battery. Coated primaryparticles, 2-7.5% by weight pristine graphene or amine-functionalizedgraphene sheets, and a small amount of surfactant (Triton-100) wereadded into deionized water to make slurries. The slurries were thenultrasonic sprayed onto glass substrate surface to form particulates.

In a set of experiments, a mixture of LiCoO₂ powder and natural graphite(100/1-10/1 weight ratio) was sealed in each of 4 ball milling potssymmetrically positioned in a high-intensity ball mill. The mill wasoperated for 0.5-4 hours to produce particulates ofgraphene-encapsulated LiCoO₂ particles.

EXAMPLE 7 Organic Cathode Active Material (Li₂C₆O₆) of a Fast-ChargeableLithium Metal Battery

The experiments associated with this example were conducted to determineif organic materials, such as Li₂C₆O₆, can be encapsulated in graphenesheets using the presently invented direct transfer method. The resultis that organic active materials alone are typically incapable ofpeeling off graphene sheets from graphite particles. However, if asecond active material (i.e. rigid particles of an inorganic material ora metal oxide/phosphate/sulfide) is implemented along with an organicactive material in a ball milling pot, then the organic materialparticles and inorganic material particles can be separately orconcurrently encapsulated to form graphene-encapsulated organicparticles, graphene-encapsulated inorganic particles, andgraphene-encapsulated mixture of organic and inorganic particles. Thisis interesting and surprising.

In order to synthesize dilithium rhodizonate (Li₂C₆O₆), the rhodizonicacid dihydrate (species 1 in the following scheme) was used as aprecursor. A basic lithium salt, Li₂CO₃ can be used in aqueous media toneutralize both enediolic acid functions. Strictly stoichiometricquantities of both reactants, rhodizonic acid and lithium carbonate,were allowed to react for 10 hours to achieve a yield of 90%. Dilithiumrhodizonate (species 2) was readily soluble even in a small amount ofwater, implying that water molecules are present in species 2. Water wasremoved in a vacuum at 180° C. for 3 hours to obtain the anhydrousversion (species 3).

A mixture of an organic cathode active material (Li₂C₆O₆) and aninorganic cathode active material (V₂O₅ and MoS₂, separately) wasball-milled for 0.5-2.0 hours to obtain a mixture ofgraphene-encapsulated particles.

Coated primary particles, 2-7.5% by weight pristine graphene oramine-functionalized graphene sheets, and a small amount of surfactant(Triton-100) were added into deionized water to make slurries. Theslurries were then ultrasonic sprayed onto glass substrate surface toform particulates. It may be noted that the two Li atoms in the formulaLi₂C₆O₆ are part of the fixed structure and they do not participate inreversible lithium ion storing and releasing. This implies that lithiumions must come from the anode side. Hence, there must be a lithiumsource (e.g. lithium metal or lithium metal alloy) at the anode. In onebattery cell herein tested, the anode current collector (Cu foil) isdeposited with a layer of lithium (via sputtering). The resulting cellis a lithium metal cell. Flexible graphite sheets, Cu foil, and graphenefluoride films were used as a heat spreader element material to enablefast chargeability.

Example 8: Graphene-encapsulated Na₃V₂(PO₄)₃/C and Na₃V₂(PO₄)₃ cathodesfor sodium metal batteries

The Na₃V₂(PO₄)₃/C sample was synthesized by a solid state reactionaccording to the following procedure: a stoichiometric mixture ofNaH₂PO₄·2H₂O (99.9%, Alpha) and V₂O₃ (99.9%, Alpha) powders was put inan agate jar as a precursor and then the precursor was ball-milled in aplanetary ball mill at 400 rpm in a stainless steel vessel for 8 h.During ball milling, for the carbon coated sample, sugar (99.9%, Alpha)was also added as the carbon precursor and the reductive agent, whichprevents the oxidation of V3⁺. After ball milling, the mixture washeated at 900° C. for 24 h in Ar atmosphere. Separately, the Na₃V₂(PO₄)₃powder was prepared in a similar manner, but without sugar. Samples ofboth powders were then subjected to ball milling in the presence ofnatural graphite particles to prepare graphene-encapsulated Na₃V₂(PO₄)₃particles and graphene-encapsulated carbon-coated Na₃V₂(PO₄)₃ particles.Coated primary particles, 5-13.5% by weight pristine graphene oramine-functionalized graphene sheets, and a small amount of surfactant(Triton-100) were added into deionized water to make slurries. Theslurries were then spray-dried to form particulates.

The particulates of cathode active materials were used in several Nametal cells containing 1 M of NaPF₆ salt in PC+DOL as the electrolyte.It was discovered that graphene encapsulation significantly improved thecycle stability of all Na metal cells studied. In terms of cycle life,the following sequence was observed: graphene-encapsulatedNa₃V₂(PO₄)₃/C>graphene-encapsulatedNa₃V₂(PO₄)₃>Na₃V₂(PO₄)₃/C>Na₃V₂(PO₄)₃. The incorporation of graphenefilms or PI-derived graphitic films, used as a heat spreader, enablesthe sodium metal cells to be recharged in less than 10 minutes at 60° C.

EXAMPLE 9 Preparation of Graphene-Encapsulated MoS₂ Particles as aCathode Active Material of a Na metal battery (fast chargeabilityenabled by a heat-spreader element)

A wide variety of inorganic materials were investigated in this example.For instance, an ultra-thin MoS₂ material was synthesized by a one-stepsolvothermal reaction of (NH₄)₂MoS₄ and hydrazine in N,N-dimethylformamide (DMF) at 200° C. In a typical procedure, 22 mg of(NH₄)₂MoS₄ was added to 10 ml of DMF. The mixture was sonicated at roomtemperature for approximately 10 min until a clear and homogeneoussolution was obtained. After that, 0.1 ml of N₂H₄.H₂O was added. Thereaction solution was further sonicated for 30 min before beingtransferred to a 40 mL Teflon-lined autoclave. The system was heated inan oven at 200° C. for 10 h. Product was collected by centrifugation at8000 rpm for 5 min, washed with DI water and recollected bycentrifugation. The washing step was repeated for 5 times to ensure thatmost DMF was removed.

Subsequently, MoS₂ particles were dried and subjected to grapheneencapsulation by high-intensity ball milling in the presence of naturalgraphite particles. An Al foil and a flexible graphite sheet wereseparately used as a heat spreader element in constructing afast-chargeable Na metal battery.

EXAMPLE 10 Preparation of Graphene-Encapsulated MnO₂ and NaMnO₂ CathodeActive Material for Fast-Chargeable Na Metal Cells and Zn Metal CellsFeaturing a Heat Spreader Element

For the preparation of the MnO₂ powder, a 0.1 mol/L KMnO₄ aqueoussolution was prepared by dissolving potassium permanganate in deionizedwater. Meanwhile, 13.32 g surfactant of high purity sodiumbis(2-ethylhexyl) sulfosuccinate was added in 300mL iso-octane (oil) andstirred well to get an optically transparent solution. Then, 32.4mL of0.1 mol/L KMnO₄ solution was added into the solution, which wasultrasonicated for 30 min to prepare a dark brown precipitate. Theproduct was separated, washed several times with distilled water andethanol, and dried at 80° C. for 12 h. Some amount of the MnO₂ powderwas then subjected to the direct transfer treatment to obtaingraphene-encapsulated MnO₂ particles.

Additionally, NaMnO₂ particles were synthesized by ball-milling amixture of Na₂CO₃ and MnO₂ (at a molar ratio of 1:2) for 12 h followedby heating at 870° C. for 10 h. The resulting NaMnO₂ particles were thensubjected to ball-milling in the presence of MCMB particles to preparegraphene encapsulated NaMnO₂ particles.

The MnO₂ particles, with or without graphene encapsulation, are alsoincorporated in alkaline Zn/MnO₂ cells. Graphene encapsulation was foundto dramatically increase the cycle life of this type of cell. TheZn-graphene/MnO₂ battery is composed of a graphene/MnO₂-based cathode(with an optional cathode current collector and an optional conductivefiller), a Zn metal or alloy-based anode (with an optional anode currentcollector), and an aqueous electrolyte (e.g. a mixture of a mild ZnSO₄or Zn(NO₃)₂ with MnSO₄ in water). Graphene films (RGO) were used as aheat spreader element in the battery cell to enable fast chargeability.

The invention claimed is:
 1. A battery charging system comprising (a) atleast one charging circuit to charge at least one rechargeable batterycell; (b) a heat source to provide heat that is transported through aheat spreader element, implemented fully or partially inside said atleast one battery cell, to heat up said battery cell to a desiredtemperature Tc before or during charging of said battery cell; and (c)cooling means in thermal contact with the heat spreader elementconfigured to enable transporting internal heat of the battery cellthrough the heat spreader element to the cooling means when the batterycell is discharged, wherein the cooling means is not in thermal contactwith the heat spreader element when the battery cell is heated by theheat source; and wherein the heat-spreader element does not receive anelectrical current from the charging circuit to generate heat inside thebattery cell for internal resistance heating of the battery cell.
 2. Thebattery charging system of claim 1, wherein said rechargeable batterycell comprises an anode, a cathode, an electrolyte disposed between theanode and the cathode, and a protective housing that at least partiallyencloses the anode, the cathode and the electrolyte, wherein saidheat-spreader element is disposed partially or entirely inside theprotective housing and configured to alternate between receiving heatfrom said heat source at a desired heating temperature T_(h) to heat upthe battery cell to the desired temperature Tc for battery cell chargingand transferring heat from the battery cell to the cooling means whenthe battery cell is discharged or provides electric power to an externaldevice or load.
 3. The battery charging system of claim 1, wherein theheat-spreader element does not receive an electrical current from saidcharging circuit to generate heat inside the battery cell for resistanceheating of the battery cell.
 4. The battery charging system of claim 1,wherein said at least a battery cell comprises at least a temperaturesensor for measuring an internal temperature of the battery and sendinga signal of said internal temperature to said charging circuit.
 5. Thebattery charging system of claim 1, wherein the heat-spreader elementacts as a temperature sensor for measuring an internal temperature ofthe battery.
 6. The battery charging system of claim 1, wherein saidheat-spreader element comprises a high thermal conductivity materialhaving a thermal conductivity no less than 10 W/mK.
 7. The batterycharging system of claim 1, wherein said heat-spreader element comprisesa material selected from a graphene film, flexible graphite sheet,artificial graphite film, Ag, Ag, Cu, Al, brass, steel, Ti, Ni, Mg alloysheet, silicon nitride, boron nitride, aluminum nitride, boron arsenide,a composite thereof, or a combination thereof.
 8. The battery chargingsystem of claim 7, wherein said graphene film contains a grapheneselected from pristine graphene, graphene oxide, reduced graphene oxide,graphene fluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, chemically functionalizedgraphene, or a combination thereof.
 9. The battery charging system ofclaim 1, wherein the heat source is heated by using laser heating,resistance heating, dielectric heating, thermal-electric heating,microwave heating, radio frequency heating, hot fluid heating, or acombination thereof.
 10. The battery charging system of claim 1, whereinthe cooling means is selected from a heat sink, a heat pipe, a vaporchamber, a stream of flowing fluid, a thermoelectric device, a heatexchanger, a radiator, or a combination thereof.
 11. The batterycharging system of claim 1, wherein the heat-spreader element is in aheat-spreading relation to an anode or a cathode of a battery cell andprovides heat thereto before or during charging of the battery cell orreceives heat therefrom when the battery cell is discharged to power anexternal device.
 12. The battery charging system of claim 1, wherein theheat source or the cooling means has a clipping means or connector meansto reversibly grip or connect with a tab of said heat spreader element.13. The battery charging system of claim 1, wherein the heat-spreaderelement has a tab protruded outside of the protective housing, whereinsaid tab is configured to controllably make thermal contact with theexternal heat source and get disconnected with the external heat sourcewhen a battery temperature reaches the desired temperature Tc.
 14. Thebattery charging system of claim 1, wherein the battery has an anodeterminal and a cathode terminal for operating the battery and theheat-spreader element is in thermal contact with the anode terminal orthe cathode terminal wherein the anode terminal or the cathode terminalis configured to receive heat from the external heat source.
 15. Thebattery charging system of claim 1, wherein the heat-spreader element isin thermal contact with the protective housing or a cap of theprotective housing.
 16. The battery charging system of claim 1, whereinthe battery is a lithium-ion battery, lithium metal secondary battery,lithium-sulfur battery, lithium-air battery, lithium-selenium battery,sodium-ion battery, sodium metal secondary battery, sodium-sulfurbattery, sodium-air battery, magnesium-ion battery, magnesium metalbattery, aluminum-ion battery, aluminum metal secondary battery,zinc-ion battery, zinc metal battery, zinc-air battery, nickel metalhydride battery, lead acid battery, lead acid-carbon battery, leadacid-based ultra-battery, lithium-ion capacitor, or supercapacitor. 17.A method of operating a battery charging system comprising multiplecharging stations, said method comprising: (a) positioning multiplerechargeable battery cells respectively in said multiple chargingstations; (b) operating at least a heat source in said battery chargingsystem to provide heat that is transported through a heat spreaderelement, implemented fully or partially inside each of said batterycells, to heat up said battery cells to a desired temperature Tc; (c)activating at least one charging circuit in said battery charging systemto charge said battery cells at or near Tc until said battery cellsreach a desired degree of charge; and (d) stop battery cell charging andbringing the heat spreader element to make thermal contact with acooling means; and wherein the heat-spreader element does not receive anelectrical current from the charging circuit to generate heat inside thebattery cell for internal resistance heating of the battery cell. 18.The method of claim 17, wherein each of said battery cells comprisestherein a heat spreader element having an end connected to an electrodeterminal of the battery cell or having a tab protruded out of aprotective housing of the battery cell and wherein said step (b)comprises bringing the electrode terminal or the tab in thermal contactwith said external heat source, allowing heat from the heat source totransfer into the battery cell for heating the battery to a desiredtemperature Tc.
 19. The method of claim 17, further comprising a step ofoperating a temperature sensor for measuring an internal temperature ofthe battery cells.
 20. The method of claim 17, wherein saidheat-spreader element comprises a high thermal conductivity materialhaving a thermal conductivity no less than 10 W/mK and wherein a timefor heating the battery cells to temperature Tc is no greater than 15minutes.
 21. The method of claim 17, wherein said heat-spreader elementcomprises a material selected from graphene film, flexible graphitesheet, artificial graphite film, Ag, Ag, Cu, Al, brass, steel, Ti, Ni,Mg alloy sheet, silicon nitride, boron nitride, aluminum nitride, boronarsenide, a composite thereof, or a combination thereof.
 22. The methodof claim 21, wherein said graphene film contains a graphene selectedfrom pristine graphene, graphene oxide, reduced graphene oxide, graphenefluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, chemically functionalizedgraphene, or a combination thereof.
 23. The method of claim 17, whereinthe step of implementing a heat spreader element inside the battery cellcomprises placing the heat-spreader element in physical or thermalcontact with the anode or the cathode for providing heat thereto. 24.The method of claim 17, wherein the heat-spreader element has a tabprotruded outside of the protective housing and wherein said step (b)comprises controllably making the tab in thermal contact with theexternal heat source and disconnecting the tab from the external heatsource when a battery cell temperature reaches the desired temperatureTc.
 25. The method of claim 17, wherein the heat-spreader element has atab protruded outside of the protective housing and wherein said step(d) comprises controllably making the tab in thermal contact with thecooling means when the battery cell is discharged.
 26. The method ofclaim 17, wherein the battery cell has an anode terminal and a cathodeterminal for operating the battery cell and the heat-spreader element isin thermal contact with the anode terminal or the cathode terminal andwherein step (b) comprises bringing the anode terminal or the cathodeterminal in physical or thermal contact with the external heat sourcefor battery charging; or wherein step (d) comprises bringing the anodeterminal or the cathode terminal in physical or thermal contact with thecooling means when the battery cell is discharged.
 27. The method ofclaim 17, wherein the heat-spreader element is in thermal contact withthe protective housing or a cap of the protective housing and said step(b) comprises bringing the external heat source to thermally orphysically contact the protective housing or the cap, supplying heatthereto for cell charging; or said step (d) comprises bringing thecooling means to thermally or physically contact the protective housingor the cap, removing heat therefrom for battery discharging.